Pump Efficiency and Head Loss... I’m at a Loss :(

Jump to latest Follow Reply
At 43 gpm, the heat pump creates about 6 psi (14 feet) of head loss.

Maybe there is an issue with the internal bypass inside the heater or with the check valve.

There might be several issues.

Getting a suction gauge reading should help diagnose the issue.

The heat exchanger tube is a pretty small diameter. So, maybe something is blocking the flow.
 
JamesW said:
At 43 gpm, the heat pump creates about 6 psi (14 feet) of head loss.

Maybe there is an issue with the internal bypass inside the heater or with the check valve.

There might be several issues.

Getting a suction gauge reading should help diagnose the issue.

The heat exchanger tube is a pretty small diameter. So, maybe something is blocking the flow.
Click to expand...

Thanks James, I ordered the gauge and will install it on Thursday morning when I get back home from work. Hopefully it will give us some more definitive answers.


Thanks again,

Brandon
 
Brandon,

Point the OFF tab up to the sky and remeasure some flow rates. Doing so takes that valve out of the equation as both the heater and bypass are 100% open. Water will flow through both legs and the flow will split according to resistance of each path. I haven’t looked back at your various charts so I’m not sure if you have posted results before. My guess is you will get slightly higher flow now that two paths are available for the water to flow through. That TEE was not plumbed correctly but it doesn’t necessarily have to be redone.

I’m not saying there aren't other issues that could be impeding water flow, I’m just wondering what the total flow rate through all return paths is when you’re not obstruction the orifice of each leg with the valves internal window.
 
Hi Matt,

Here is the info you requested. I pointed the ‘off’ position straight up, sending water to the heater and the bypass. I did notice the flapper in the heater bypass never opened-up, leading me to believe 100% of the water went through the bypass. I closed the bypass and sent 100% of the water to the heater and the bypass opened-up. I did dissamble the valve and make sure everything was correct and it was. With the ‘off’ position pointing straight-up, the stopper was straight-up as well. When rotating the handle to the heater and the bypass, the stopper followed the ‘off’ position to the respective pipe.

RPMGPMFilter PSIPump PSIPump less Filter PSI
100016033
125025041
150033176
175040396
2000475127
2250547158
25005991910
275064112312
300069132714
325074163216
345078183618


Thanks again,

Brandon
 
So what’s the flow at full speed with the filter in recirculate and the splitter set with both the heater and bypass at full open ?

Sorry, I know we’re making you do lots of tests but this last one is the highest possible flow rate your system can achieve.

I’d like to see what that number is and if Mark thinks it’s what should be expected given your plumbing setup.
 
The maximum theoretical suction is 14.7 psi.

Even before that, the pump will begin cavitating.

Does the pump sound like it's pumping gravel at full speed?

There might be something clogging the multiport.

Is there a strainer/diffuser inside the filter where the water enters the filter?
 
JoyfulNoise said:
So what’s the flow at full speed with the filter in recirculate and the splitter set with both the heater and bypass at full open ?

Sorry, I know we’re making you do lots of tests but this last one is the highest possible flow rate your system can achieve.

I’d like to see what that number is and if Mark thinks it’s what should be expected given your plumbing setup.
Click to expand...

Hello Again,

With the MPV in recirculate, pump at 3450 RPM I was able to achieve 90 GPM @ 34 PSI on the pump. This was achieved with the bypass valve pointing ‘off’ straight up, sending everything to the heater and bypass. I looked at the check valve on the return side of the heater and there was no water coming through, the valve appeared to be in the closed position.


Thanks,

Brandon

- - - Updated - - -

JamesW said:
The maximum theoretical suction is 14.7 psi.

Even before that, the pump will begin cavitating.

Does the pump sound like it's pumping gravel at full speed?

There might be something clogging the multiport.

Is there a strainer/diffuser inside the filter where the water enters the filter?
Click to expand...

Hi James,

at 3450 RPM, there is no “pumping gravel sound” the pump is loud in terms of the motor running, but nothing abnormal or anything that would cause for pause. The Pentair VSF has the stratiner basket in the pot and it is clean of leaves and debris. There is nothing between the pump and filter besides the MPV.


Thanks again,

Brandon
 
90 gpm is close to what I would expect from that plumbing setup so it is pretty clear that the filter is adding quite a bit of head loss (not to mention the heater too).
 

Enjoying this content?

Support TFP with a donation.

Give Support
It’s a small filter in my opinion. My pool is roughly the same size as the OP’s and I have a QuadDE-100. I don’t have the ability to measure flow (I refuse to use ScreamLogic !!....and I don’t have a VSF pump) but I have never had any flow issues with my system. I don’t have a bypass on my heater and I do not have an MPV, so my plumbing is quite a bit simpler.

From what little I’ve read, the Quad’s are only slightly worse in terms of head loss than a standard cartridge filter, so my gut says there’s something in that MPV that’s causing an issue.
 
So based on these new findings, how can well tell if it’s a filter, MPV and/or heater issue causing the issue(s)? Do I need to do anything to the heater? I haven’t run it yet, but it is receiving power? I’m wondering if the heater needs to be turned-on so that it can adjust any of it’s internal electronics? The multi port has a ton of screws and looks like a big valve. Should I disassemble and check for any issues?


Thanks,

Brandon
 
Actually, I no longer think there is an "issue" with any of the equipment. You just have chosen some pieces with fairly large head loss characteristics. The three major components are as follows:

Heat Pump -> Equivalent to 167' of 2" pipe
MPV -> Equivalent to 133' of 2" pipe
DE60 -> Equivalent to 100' of 2" pipe

The DE filter is not that bad and is similar to a cartridge but when you add the MPV, the combined head loss is more than double a cartridge filter. Also, the heat pump has more than double the head loss of a typical gas heater. Combined, it really puts a damper on flow rates.

https://www.pentair.com/content/dam/extranet/product-related/product-manuals/pool-and-spa-equipment/filters/QUADDEOwnersManualEnglish.pdf
https://www.pentair.com/content/dam/extranet/product-related/product-manuals/pool-and-spa-equipment/valves/Hi%20Flow%20Side%20Mounted%20Backwash%20Valve%20Installation%20Guide%20English.pdf
https://www.pentair.com/content/dam/extranet/product-related/product-manuals/pool-and-spa-equipment/ultratemp/UltraTemp_Heat_Pump_Installation_and_Users_Guide_English.pdf
 
Thanks Mark. Should I speak with my PB about eleminating the MPV and/or upgrading the filter to an 80 or 100? As for the heater, does the chart I supplied earlier look correct given the filter and MPV losses? Also, would it make sense for no water to be flowing through the heater check valve when I’ve git flow going to heater and bypass?


Thanks again,

Brandon
 
My suggestion is to remove the multiport and put a 3 way valve so that you can go to waste if necessary.

I would also keep the flow to a maximum of 40 gpm.

30 to 35 gpm is more than enough for the heat pump.

Assuming a 120,000 btu/hr heat transfer, at 30 gpm, the heat rise will be 8 degrees Fahrenheit.

At 50 gpm, the temperature rise will be 4.8 degrees Fahrenheit.

There's an insignificant difference in heat transfer between 30 and 50 gpm.

I would also keep the external bypass closed so that the flow goes to the heat pump.

I would remove the chlorinator and the check valve.
 
Wow! That MPV really adds a lot of loss....I’m shocked it’s so high.

Brandon,

One benefit of running an oversized Quad filter for me is that I never backwash the filter. I simply open it up and clean it out twice per year. I have a simple plunger style backwash valve but the honest truth is it is practically useless. In fact, last season it started leaking because the o-rings needed replacement and I thought to my myself that it was such a waste of time and a headache that I should just replumb the pad and ditch the valve. There are many people here that plumb a QuadDE like a cartridge filter with no backwash valve at all. I don’t know how your Quad60 will fair over time with its loading frequency but, if you can live without backwashing, then ditching the MPV altogether might be a viable alternative. In reality, backwashing does a very poor job of cleaning out a filter and it’s always better to fully clean it out and add the exact right quantity of DE as oppose to trying to guess how much DE was sent out the backwash line (it’s less than half).

You may just need to run the pool for a while to figure out how best to work it. You may be able to live with what you have in the setup. Time will tell you what really needs fixing.....

Oh, and about that bonding TEE, I’m not sure it’s useful at all. If the pool was constructed properly and the rebar in the shell was bonded correctly, then there’s no need for an additional water bond. PB’s seem to do the strangest things nowadays with water bonds and zinc anodes, stuff that flies in the face of good science and engineering. It’s not going to harm anything being there (unless there’s some hunk of metal in that TEE slowly corroding away) but it’s not really useful either.
 
TxHr said:
Thanks Mark. Should I speak with my PB about eleminating the MPV and/or upgrading the filter to an 80 or 100?
Click to expand...
Definitely an option.

As for the heater, does the chart I supplied earlier look correct given the filter and MPV losses?
Click to expand...
Yes. This matches the measured head loss curves in the manuals.

Also, would it make sense for no water to be flowing through the heater check valve when I’ve git flow going to heater and bypass?
Click to expand...
Yes, because the HP is much more restrictive, very little flow rate will actually go in that direction.
 
Thank you to everyone for the information and suggestions. As for the DE 60, would a DE 80 or DE 100 have a better flow and less head? Before I go asking for help from my PB, I want to make sure the request will aid in the flow and decreased head.


Thanks again,

Brandon
 
The head loss of the larger filter is about the same. However, the frequency of cleaning is the biggest difference. This could be very important if you do not have a MPV.
 
The larger filter will give you slightly better flow. However, as long as the flow is going to be kept below 50 gpm, I don't think that it's worthwhile to go to a bigger filter.

If it was a new install, I would choose the 100, but I wouldn't pay to replace a working filter.
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply